The invention is generally related to electric motors, particularly electronically-commutated, brushless direct current (BLDC) motors. Motors of this kind can be used in a variety of applications, examples being in automotive engineering for fans, cooling pumps or steering system support. Other application areas include ventilator fans in power supply units, or spindle motors in disk drives for data processing systems, just to mention a few.
A brushless DC motor basically consists of a shaft, a rotor assembly equipped with one or more permanent magnets arranged on the shaft, and a stator assembly which incorporates a stator component and phase windings. Bearings are mounted at an axial distance to each other on the shaft to support the rotor assembly and stator assembly relative to each other.
One kind of a stator component for electric motors known in the art consists of sheet metal comprising a plurality of steel plates which are laminated together. Although a sheet metal stator core has advantages of high saturation magnetic flux density and relative inexpensiveness, there has been a problem in that eddy current in the metal plates increases rapidly with increase in operating frequency of the motor. As a result of this, heat generation in the sheet metal core and magnetic core loss increase rapidly.
It is a further drawback that variations to the design of the sheet metal cores are limited by the manufacturing process.
It is also known in the art, e.g. disclosed in EP 0 869 517 B1, to use so called powder or dust cores which consist of pressed ferromagnetic metal powder. In contrast to a steel plate core, a powder core is a core produced by pressing a metal powder mixture. In this process, a binder, for example, a resin is appropriately added to the metal powder. After pressing, hardening treatment by heating, etc., so-called curing, may be performed in order to cure the added resin and the like. Examples of metal powders to be used include ferromagnetic metal powders, for example, an iron powder, an iron-based powder, or a nickel powder. Since the powder core uses a metal powder as a raw material and a resin, having superior insulation property, as a binder, the core loss in high frequencies is lower than that of an iron core using an electrical steel plate.